Field of the Invention
The present disclosure generally relates to modified insecticidal Bacillus thuringiensis proteins and genes coding for the same with improved insecticidal activity.
Description of the Related Art
Order lepidoptera includes butterflies and moths. At present there are estimated 200,000 species of lepidoptera worldwide, which accounts for about 10% of the total described species of the animal kingdom. It is one of the most widespread and widely recognizable insect orders. In Korea, about 3,200 species have been found and account for about 40% of the crop pests. Lepidoptera pests contribute a major share to the crop loss. Larvae of these pests are very voracious polyphagous particularly at the younger instars causing a drastic damage to the crop foliage and produce.
For the last five decades, these pests have been mostly controlled by chemical and synthetic pesticides. But the indiscriminate use of the chemicals has raised serious health and environmental safety concerns. This has led to a paradigm shift in the pest control to the biopesticides.
Among biopesticides, Bacillus thuringiensis (BT) and its endotoxins genes have been widely studied and developed for the pest control.
Bacillus thuringiensis is a gram positive bacterium that produces proteinaceous crystalline inclusions during sporulation. These crystal proteins are often highly toxic to various insects such as Lepidoptera, Coleoptera and Diptera.
Insecticidal BT crystal proteins can differ extensively in their structures and insecticidal activities. These proteins are encoded by genes typically located on large plasmid, greater than 30 MDa in size. Thus a number of BT toxin genes have been isolated and characterized.
Traditional commercial BT biopesticide products are purified BT strains isolated from natural sources or genetically modified strains which are disclosed in U.S. Pat. Nos. 5,080,897 and 4,935,353.
Also disclosed are various transgenic crops genetically modified to express cry1-type endotoxin for Cottons (Perlak et al., Biotechnol. 8:939-943, 1990), Rice (Fujimoto et al., Biotechnol. 11:1151-1155, 1993), Corns (Bourguet et al., Proc. Biol. Sci. 267:117-122, 2000), Tobaccos (Strizhov et al., Proc. Natl. Acad. Sci. U.S.A. 24:15012-15017, 1996), Tomatos (Perlak et al., Proc. Natl. Acad. Sci. U.S.A. 88:3324-3328, 1991), Beans (Stewart et al., Plant Physiol. 112:121-129, 1996), and Alphafas (Strizhov et al., Proc. Natl. Acad. Sci. U.S.A. 24:15012-15017, 1996).
Although Bt products have significant advantages as biological control agents, the conventional use of Bt insecticides have been faced with some limitations such as a narrow host spectrum, a short shelf life and the development of pest insect resistance.
Korean Patent No. 280380 relates to an endotoxin protein from BT NT0423 strain and insecticidal composition comprising the same. Korean Patent No. 432140 relates to an endotoxin protein from K-1 strain and insecticidal composition comprising the same. Korean Patent No. 436026 relates to a BT KFRI-2 strain having pesticidal activity against lepidoptera and diptera insects and insecticidal composition comprising the same. Korean Patent No. 599414 relates to a BT K-3 strain expressing novel endotoxin and insecticidal composition comprising the same. Also disclosed is a method for introducing two genes from BT by gene stacking to transgenic rice (Yang et al., Pest Manag. Sci. 67:414-422, 2011) and a transgenic mustard expressing cry1A and cry1C (Cao J et al., Plant Cell Rep. 27:479-487, 2008)
None are disclosed in the prior arts regarding endotoxins having broader host range while maintaining or showing superior insecticidal activity against Order lepidoptera.
Thus there exist needs to develop strategies that will delay or counteract the resistance at the molecular level by developing novel endotoxin genes.